Fluid pump or fluid motor

ABSTRACT

A fluid motor or fluid pump of the piston or vane type having a plurality of pistons or vanes, a mounting means for said pistons or vanes, a cam ring, a rear cover, a valve plate interposed between said rear cover and said mounting means and a valve mounted outside of said rear cover. A plurality of annular grooves having openings on an inner side surface of the rear cover are formed in said rear cover. Each groove has a port opening on outer side of the rear cover. The valve plate with passages is disposed between the mounting means and the rear cover for covering said annular grooves and for communicating passages formed in said mounting means with said annular grooves. Between the valve plate and the annular grooves, a plurality of rings or inner and outer rings can be mounted for sliding contact with said valve plate. By changing the connection of said annular grooves with a power source by means of said valve and/or by rotating said inner and outer rings the connection or disconnection of said grooves with said passages are selected.

Unite States Patent Oguni Mar. 12, 1974 FLUID PUMP OR FLUID MOTOR [75] inventor: Hiroshi Oguni, Akashi, Japan [73] Assignee: Kawasaki Jukogyo Kabushiki Kaisha, Kobi-shi, Hyogo-kcn, Japan 22 Filed: Sept. 24, 1971 211 Appl. No.: 183,324

[301 Foreign Application Priority Data Primary ExaminerCarlton R. Croylc Assistant Examiner-Gregory P. LaPointe Attorney, Agent, or FirmToren and McGcady [57] ABSTRACT A fluid motor or fluid pump of the piston or vane type having a plurality of pistons or vanes, a mounting means for, said pistons or vanes, a cam ring, a rear cover, a valve plate interposed between said rear cover and said mounting means and a valve mounted outside of said rear cover. A plurality of annular grooves having openings on an inner side surface of the rear cover are formed in said rear cover. Each groove has a port opening on outer side of the rear cover. The valve plate with passages is disposed between the mounting means and the rear cover for covering said annular grooves and for communicating passages formed in said mounting means with said annular grooves. Between the valve plate and the annular grooves, a plurality of rings or inner and outer rings can be mounted for sliding contact with said valve plate. By changing the connection of said annular grooves with a power source by means of said valve and/or by rotating said inner and outer rings the connection or disconnection of said grooves with said passages are selected.

1 Claim, Iii-Drawing Figures sirssJas PATENTEBHAR 12 m4 SHEET 1 BF 6 INVENTOR HI oeum (7mm amid 7c 0o? ATTORNEYS PATENIEB m 2 mm SHEEI 2 0F 6 INVENTOR HIROSHI oeum (95m? dm'c/%%Mc? ATTORNEYS mammumz mu 3.795136 SHEEI 5 0F 6 Fig.1?

130 135a W MO 143a 143D 133C 14 d 135b 136b 143 INVENTOR HIROSHI 06UNI ATTORNEY$ INVENTOR HIROSHI OGUNI BY Tam? awe/M 710? ATTORNEYS FLUID PUMP OR FLUID MOTOR This invention relates to a fluid pump or fluid motor of the piston or vane type.

An object of this invention is to provide a pressure distribution valve means for a fluid pump or fluid motor of the piston or vane type which is effective to vary the volume of effective working liquid for each revolution so as to permit the pump or motor to operate as a variable volume fluid pump or fluid motor.

Another object of the invention is to provide a working liquid distribution mechanism for a fluid pump or fluid motor which comprises a valve plate to accomplish the object.

Additional objects as well as features and advantages of this invention will become evident from the description set forth hereinafter when considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a sectional view of a conventional motor or pump of the piston type;

FIG. 2 and FIG. 3 are fragmentary sectional views taken along the lines XX and YYlY2-Y3Y4-Y5 of FIG. 1 respectively;

FIG. 4 is a sectional view of essential portions of the fluid pump or fluid motor according to the first embodiment of this invention;

FIG. 5 is a fragmentary sectional view taken along the line Z-Z of FIG. 4;

FIG. 6 and FIG. 7 are views in explanation of the operation of this invention;

FIG. 8 is a sectional view of essential portions of the fluid pump or motor according to the second embodiment of this invention;

FIG. 9, FIG. 10 and FIG. 11 are sectional views taken along the line X1X2-X3-X4-X5X6 of FIG. 8 and showing the parts in different states;

FIG. 12 is a vertical sectional view of essential portions of the fluid pump or motor according to the third embodiment of this invention; and

FIG. 13 is a view in explanation of the arrangement of essential portions of FIG. 12 as seen from the right side.

FIG. 1 to FIG. 3 illustrate a fluid pump or fluid motor of the piston typeof the prior art. Essential portions of the device functioning as a fluid motor will be described.

In FIG. 1, a fluid under pressure supplied through a working fluid inlet port 1 passes through an annular passage 2, ducts 3, ports 5 formed in a valve plate 4 and passages 7 formed in a mounting means, for example, in a cylinder body 6 in the indicated order to move into cylinder chambers 8. The working fluid in cylinder chambers 8 pushes and moves pistons 9 so as to bring rollers 10 mounted at the heads of pistons 9 into pressing engagement with a cam surface of a cam ring 20.

Assuming that rollers 10 of pistons 9 are positioned against a lower dead point A1 of the cam surface and the cylinder body rotates in the direction of the arrow like the piston 9a and the roller 10a shown in FIG. 2, piston 90 will be pushed radially outwardly in a cylinder chamber 8a to rotate cylinder body 6 and a main shaft 14 in a section ranging from the lower dead point Al to an upper dead point B1. In this section, the port 5 of valve plate 4 shown in FIG. 3 and the passage 7a in cylinder body 6 are maintained in communication with each other.

While piston 9a in FIG. 2 moves through a section ranging from an upper dead point B] to a next lower dead point A2 of the cam surface, passage 7a in cylinder body is maintained in communication with the port 15 of valve plate 4 shown-in FIG. 3, and piston 9a is moved radially inwardly in cylinder chamber 8a so as to move the fluid in the cylinder chamber through port 15, duct 16 and annular passage 17 in the indicated order so as to discharge the fluid through an outlet port 18. The fluid can be moved from an inlet port 18 to an outlet port 1 reversely.

In the known device described above, an effective working fluid volume ql for each revolution of the motor can be expressed by the following formula:

ql =1r/4d -Z'S'm where d is the effective diameter of pistons, Z is the number of pistons, S is the stroke of pistons which may vary depending on the shape of the cam, and m is the number of strokes of pistons for one revolution of motor (which is equal to the number of elevated portions of the cam).

Thus, ql is a constant and the motor is a constant volume motor.

In special cases, the motor may be provided with four or six inlet and outlet ports and fluid may be supplied and discharged selectively through these ports by operation from outside so as to vary the number of effective working pistons. However, this arrangement entails a complex valve and other switching mechanism which isdifficult to manufacture and troublesome to operate.

In the known device described, working liquid inlet and outlet ports 1 and 18, annular passages 2 and 17 and a number of ducts which maintain the annular passages in communication with a number of ports formed in valve plate 4 for distributing working liquid are all provided in a rear cover 19 of the motor. In producing the rear cover of the aforementioned construction by casting in a mold, difficulties are faced with in supporting a core for forming annular passages 2, 17. Besides, special consideration must be paid to the flow of molten metal because the ducts for maintaining the annular passages in communication with the ports in the valve plate are complex in construction. In spite of special attention, blows and pin holes are liable to occur in the casting. In addition, a lot of skilled manual attention is required for production.

This invention obviates the aforementioned disadvantages of the prior art device described.

This invention is characterized in one aspect by the provision, as shown in FIGS. and 5, of inner and outer or two annular grooves 30 and 31 having openings on the inner side of rear cover 19, working liquid inlet and outlet ports 32 and 33 extending from the outer side of the rear cover to the bottoms of the respective annular grooves, a valve plate 34 positioned on one side against one side of cylinder body 6 and on the opposite side within an annular recess in the rear cover 19 extending across the annular grooves 30 and 31 and being slidable relative to the cylinder body, so as to provide a cover to the openings of the annular grooves, and a number of passages 35 and 36 formed in valve plate 34 so as to communicate a number of working liquid passages 7 with either of the two annular passages, said passages 7 opening in one side of cylinder body 6 to communicate with respective cylinder chambers 8.

The annular grooves 30 and 31 according to this invention are not enclosed passages formed in rear cover 19 like annular passages 2 and 17 of the conventional device but are open on one side. This eliminates the use of a core in producing the rear cover in a molding operation. Annular grooves 30 and 31 can be formed by machining the rear cover after it is produced by casting in a mold.

The mechanism provided by this invention does without the ducts 3 and 16 of conventional device which are provided between the ports 5 and of valve plate 4 and annular passages 2 and 17 respectively. This eliminates the need to pay special attention to the flow of molten liquid in the molding operation. According to this invention, passages 35 and 36 are provided in valve plate 34 in place of ducts 3'and 16, so that machining can be carried out positively by simple means.

The valve plate 34 according to this invention is slightly displaced peripherally with respect to the cylinder body of the motor, so that it is characterized by being able to regulate work output (volume) without influencing in any way the operation of switching work fluid which is the inherent function of the valve plate.

Assuming that the numeral 20 in FIG. 6 designates the cam surface of FIG. 2 and the cylinder body rotates in a direction designated 0, the ducts 35 and 36 in the valve plate are arranged such that, if the valve plate were mounted in its normal position, fluid under pressure would be supplied to the cylinder chambers when the pistons move from a lower dead point A to an upper dead point B of the cam surface, and the fluid in the cylinder chambers would be discharged therefrom when the pistons move from the upper dead point B to a next lower dead point C. The output of the pistons at this time would be proportional to the hatched area in the figure.

If valve plate 34 were displaced from its normal position such that the-supply of fluid under pressure to the cylinder chambers is initiated when the pistons are indexed with a point 01 disposed posterior to the lower dead point A and cut off when the pistons pass the upper dead point B and are indexed with a point 02 as shown in FIG. 7, the fluid under pressure would not perform outside work while the pistons move from A to 61 and would interfere with the introduction of the pistons into the respective cylinder chambers while the pistons move from B to 62 so that the output of the piston would be negative. Thus, it will be evident that the displacement of the valve plate from its normal position results in a reduction in the rotational output transmitted to the outside when the device functions as a motor and in a reduction of volume when the device functions as a pump, thereby permitting to regulate output or volume.

While the embodiment described above refers to a fluid motor, it will be understood that the present embodiment can also be incorporated in a pump, and that the invention can be incorporated in a fluid motor or fluid pump of not only the piston type but also the vane type.

The aforementioned annular grooves and 31 may be modified such that, when cylinders are arranged in a plurality of rows disposed normal to the output (input) shaft or when effective volume is made variable while the cylinders are arranged in a single row, the number of annular grooves may be increased from one set to a plurality of sets, with one set being employed to close a set of passages to reduce the number of effectively working pistons.

In FIGS. 4 and 5, the numeral 36' designates a channel interposed between annular grooves 30 and 31 opening at one end in the inner side of the rear cover. Said channel 36 is normally maintained, through a small duct 37 in communication with one of the annular grooves 30 and 31 which is connected to the high pressure fluid side, so as to press against a back side of the valve plate a ring 38 mounted at the open end of said channel 36'. Thus, ring 38 is pressed against the valve plate by virtue of pressure differential between the annular grooves 30 and 31, thereby preventing leakage of fluid.

The numeral 39 designates a contact plate mounted on the opening side of passages 11 through which part of the fluid under pressure in cylinder chambers 8 is led to a side of the cylinder body opposite to the side thereof on which valve plate 34 is disposed. Contact plate 39 is intended to perform the function of pressing the cylinder body against valve plate 34 by virtue of the pressure of working fluid permitted to leak between contact plate 39 and As the valve plate 34 is slidable about the axis of the cylinder body a clearance between the slide surfaces on the contact surfaces of the cylinder body 6 and the valve plate 34 and/or of the cylinder body 6 and the contact plate 39 can be optimally adjusted depending on the fluid pressure acting on the back surface of the valve plate 34. Therefore, leakage at the contact surfaces and seizure caused by metal contact can be prevented. cylinder body 6.

In the embodiment shown in FIG. 8 which shows, on an enlarged scale, a portion of rear cover 19 shown in FIG. 1, annular grooves and 131 are formed on an inner side of rear cover 19 to communicate with inlet and outlet ports 132 and 133 respectively which are formed on an outer side of the rear cover. Annular grooves 130 and 131 have a common opening which is disposed on the inner side of rear cover 19 and covered with valve plate 134. Rings 140 and 141 are mounted on outer and inner peripheral surfaces of a portion of valve plate 134 which projects into annular grooves 130 and 131, so that rings 140 and 141 can move in sliding motion in the respective grooves. By selectively varying the arrangement of passages (subsequently to be described) formed in valve plate 134 and ducts (subsequently to be described) formed in ring 140 and 141 and/or passages 7, the present invention permits to vary the volume of effective working fluid of the motor as illustrated in FIGS. 9 to 11.

FIG. 9 shows the arrangement of the passages in the valve plate and the ducts in the inner and outer rings. Provided in inner ring 141 are ducts 143 which are disposed in positions corresponding to one-half pitch of elevated portions of the cam surface and comprise a duct 143a aligned with the center line 0A1 of an elevated portion of the cam surface, a duct l43b aligned with the center line OBI of a depressed portion of the cam surface, and a duct 143C aligned with the center line 0A2 of an elevated portion of the cam surface.

Formed in valve plate 134 are the passages 136a, a, 136b, 135b which are formed in the valve plate 134 to communicate with passages 7 on the cylinder body as shown in FIG. 8. When cylinder body 6 rotates through a section of the cam surface between 0A1 and OBI corresponding to one-half pitch of elevated portions of the cam surface, a passage 7 is indexed with the sage 7 is indexed with the passage 135a; and when it rotates through a section of the cam surface between 0A2 and next center line which is spaced apart from OA2 by one-half pitch of elevated portions of the cam surface, the particular passage 7 is indexed with the passage 136b.

Formed in outer ring 140 in positions corresponding to elevated and depressed portions of the' cam surface in FIG. 9 are a duct 142d, duct 142a, recess 146, duct 142b and duct 142C in the indicated order. The spacing between ducts l42dand 142a corresponds to one-half pitch of elevated portions of the cam surface; the spacing between ducts 142a and 14211 corresponds to one pitch of elevated portions of the cam surface; and recess 146 is disposed midway between ducts 142a and 142b or spaced apart from both ducts 142a and l42b a distance corresponding to one-half pitch of elevated portions of the cam surface, the recess 146 having an opening which is disposed adjacent an outer peripheral surface of valve plate 134.

Between each passage 136a, 136b, opened to the inner peripheral surface of the valve plate 134 opposed to the inner ring 141 the passages 135a, 135b, 1350 opened to the outer peripheral surface of the valve plate 134 opposed to the outer ring 140 are disposed as shown in FIG. 9. The passage 135a is connected with one of the ducts 142 of the outer ring 140 and with one of the passages 7, while the passage 135b with two passages connected with each other is connected with the adjacent ducts 142 of the outer ring 140 and one of the common passages 7. The passages 136a, 136b are formed with two passages connected with each'other at the opening communicated with-the passage 7, and are opened to the inner surface andthe outer surface of the valve plate 134. The passages 1360, 136b and the passages l35a, 135b respectively are opened near to each other on the outer peripheral surface of valve plate 134 so as to connect each other at the recesses 146 of the outer ring. The passages 1350, 135b and 1360, 13611 are so disposed that the passages 136a, 1361) are connected with the ducts 143a, 143C of the inner ring 141 respectively and the passage 7 in normal, that the passage 136a is connected with the duct 143d of the inner ring 141 and the passage 7, the passage 136b with the recess 146 of the outer ring 140 and with the, passage 7, the passage 135a with the duct 142d and with the passage 7 and the passage 135b with the recess 146, and the duct l42b of the outer ring 140 and with the passage 7, when the inner ring 141 and the outer ring 140 are rotated relatively to valve plate 134 from their positions in FIG. 9 in the direction of an arrow at a distance corresponding to one-half pitch of elevated portions of the cam surface as shown in FIG. 10, and that the passage l36a is connected with the duct l43b of the inner ring 141, with the passage 7 and with recess 146 of the outer ring 140, the passage 13612 with the duct 143d of the inner ring 141 and with the passage 7, the passage 135a with the recess 146 of the outer ring 140 and with the passage 7 and the passage 13512 with the ducts 142a and 142:! of the outer ring 140 and with the passage 7, when the inner ring 141 and the outer ring 140 are rotated relatively to valve plate 134 from their positions in FIG. 9 in the direction of an arrow or a distance corresponding to one-half pitch of elevated portions of the cam surface as shown in FIG. 11.

Let us assume that, in FIG. 9, the pistons and cylinder body rotate counter clockwise 'as indicated by an arrow, working fluid is supplied to inner annular groove 131 through inlet port 133 shown in FIG. 8, and outer annular groove is maintained in communication with the pressure discharge side through outlet port 132. The working fluid introduced through inlet port 133 shown in FIG. 8 into inner annular groove 13] passes through ducts 143a, 1436 in inner ring 141, and the passages 136a, 1361) in valve plate 134 to move into the passages 7 to cylinder chambers 8 formed in cylinder body 6 which are each moving from the lower dead point to the upper dead point of the cam surface. As a result, the working fluid moves the pistons upwardly in the corresponding cylinder chambers 8 to do work.

On the other hand, the passages 7 to cylinder chambers 8 of cylinder body 6 which are each moving from the upper dead point to the lower dead point of the cam surface so as to move the corresponding pistons radially inwardly in respective cylinder chambers 8 are maintained in connection with outlet port 132 through passages 1350, 135b in valve plate 134, ducts 142a, l42b in outer ring and outer annular groove 130. As a result, the working fluid in the respective cylinder chambers is discharged from the device.

The device operating as aforementioned functions as a motor of the constant volume type as is the case with the motor shown in' FIG. 1. In this operation, ducts 143b formed in inner ring 141 and shown in broken lines and ducts 142b formed in outer ring 140 and shown in broken lines are not put to service. The aforementioned ducts are put to service when the device functions as a motor of the variable volume type as presently to be described.

Accordingly, it will be seen that, if the inner and outer rings are rotated relative to the valve plate interposed therebetween the passage 144a on the pressure supply side or the pressure discharge side and the passages 135a on the pressure discharge side or the pressure supply side disposed near to one another on the outer periphery of the valve plate can be interconnected through the respective arcuate recesses 146a and the adjacent two cylinder chambers 8 are connected to each other, so that the effective working fluid volume can be varied.

FIG. 10 shows the motor in a state in which inner ring 141 and outer ring 140 are rotated relative to valve plate 134 from their positions in FIG. 9 in the direction of an arrow 0 a distance corresponding to one-half pitch of elevated portions of the cam surface and the port 133 is pressure supply side and the port 132 is pressure discharge side.

FIG. 11 shows the motor in a state in which the inner and outer rings are rotated in the opposite direction to that in FIG. 10, a distance corresponding to one-half pitch of elevated portions of the cam surface relative to FIG. 9 and the port 133 is connected to pressure discharge side and the port 132 is connected to pressure sage 1350 on the pressure supply side through a recess 146 so as to thereby shortcircuit the path of movement of working fluid.

No fluid under pressure is supplied to the pistons in the cylinder chambers which are connected to the arcuate recesses which shortcircuit the path of movement of working fluid as aforementioned, so that such pistons do not perform an effective motor action. The effective working fluid volume in this case can be expressed by the following formula:

ql 1r/4 d Z. S. (m-m) where m is the number of piston strokes which do not function effectively. Thus,

the motor functions as a motor of the variable volume type.

The device shown in FIG. 8 is much easier to manufacture than the device shown in FIG. 1. In the device of FIG. 1, annular passages 2 and 17 and all the ducts leading from the annular passages to the velve plate should all be provided in the rear cover of the motor. In the device of FIG. 8, however, the inner and outer annular grooves have openings on the rear cover side so that the annular grooves in FIG. 8 are much easier to form by machining than the annular passages of FIG. 1 which are hidden in the rear cover and have no opening. The valve plate can be readily worked on to form passages therein by machining. Formation of passages in the valve plate is thus much easier than formation of ducts in the rear cover which is produced by casting in a mold. I

The present embodiment has been described with reference to an embodiment which operates as a motor. It is to be understood, however, that the embodiment can be incorporated in a fluid pump with good results. The embodiment also can have application not only in motors and pumps of the radial piston type but also in motors and pumps ofthe axially piston type. The annular grooves and inner and outer rings may be of different shape and arrangement than those shown and described herein depending on the type of motor or pump in which the invention is incorporated.

This invention also can have application with good results in the valve plate of a fluid device which is adapted to deliver fluid or do work by increasing and decreasing thevolume of an oil chamber surrounded by vanes.

The embodiment shown and described above permits to produce rear cover 19 more readily than in conventional fluid motors or pumps, and is effective to vary the volume of a motor or pump by rotating the valve plate 134. In the embodiment shown in FIGS. 12 and 13, a plurality of pairs of outlet and inlet portsand a plurality of pairs of annular grooves maintained in communication with the outlet and inlet ports are provided, so as to readily vary the volume of a motor or pump. This embodiment permits to obtain a compact overall size in a fluid motor or pump in spite of the fact that a plurality of pairs of annular grooves are provided. As shown, the openings of an inner pair of annular grooves on an inner surface of the rear cover and the openings of an outer pair of annular grooves on an inner surface of the rear cover are disposed in different planes. However, this is not essential and the openings may be disposed in the same plane.

As shown in FIGS. 12 and 13, two pairs of outlet and inlet ports 222, 225, and 228 and 231 are formed in rear cover 19 which are maintained in communication with two pairs of coaxial annular grooves 223, 226 and 229, 232. The openings of annular grooves 223, 226 are formed in a position disposed deeper in the rear cover than the openings of annular grooves 229, 232. The openings of these two pairs of annular grooves are closed by the outer side surface of valve plate 221 which is formed with a projection in the central portion and offset shoulders on opposite sides of the projection. The valve plate is juxta'posed at its inner side surface with the side wall of the cylinder body 6.

As shown in FIG. 12, ducts 224, 227, 230 and 233 are formed in the valve plate to maintain communication between the aforementioned annular grooves and the passage 7 formed in the cylinder body 6. Each one of said ducts 224, 227, 230 and 233 is disposed between the elevated portion and the depressed portion of the cam surface. The passages 7 are disposed for every cylinder chamber.

FIG. 13 shows the relative positions of passages 7 formed in cylinder body 6, ducts 230, 224, 227 and 233 formed in the valve plate for connecting passage 7 to annular grooves 229, 223, 226 and 232, and outlet and inlet ports 228, 222, 225 and 231 as seen from the right side of FIG. 12.

This embodiment has a plurality of pairs of annular grooves and a plurality of pairs of outlet and inlet ports as aforementioned. Thus, it is possible by changing the connection of a valve mountedoutside of this motor to use ports 228 and 225 as fluid supply ports or fluid dis charge ports and to use ports 222 and 231 as fluid discharge ports or fluid supply ports (first case) or to use ports 225 as a fluid supply or discharge port and to make the other ports 228 to communicate with port 231 so as to bypass the fluid while the port 222 is used as a discharge or supply port (second case). In these cases, if the quantity of fluid supplied or discharged through various passages in the valve plate is uniform, a rate of the effective working fluid volume causing the pistons to operate will be 1 in the first case as against 0.5 in the second case.

A relation similar to the relation described above can be established by selecting any combination of two ports as desired from ports 231, 225, 222 and 228.

When a fluid under pressure is supplied through port 225, a thrust Fa is produced in annular groove 226 in an amount corresponding to the area of the annular groove so as to cause valve plate 221 to press against cylinder body 6. On the other hand, this fluid under pressure is partly leaked on its way to cylinder passages 7 through ducts 227 to form an oil film. Therefore, it is possible to balance pressure by suitably selecting the areas of contact in the two portions. Balance may be struck between thrust and fluid pressure in the similar manner with respect to annular groove 232. There is, thus, no danger of throwing thrust and fluid pressure off balance by the combination of ducts.

While the embodiment has been shown and described with reference to a motor, it is to be understood that the device of the same construction can perform a pumping operation. This invention also can be incorporated in a fluid motor or pump of the axial piston type and a fluid motor or pump of the vane type in which the area of an oil chamber surrounded by vanes is increased and decreased.

What we claim is:

1. A fluid motor or fluid pump comprising a plurality of working members cooperating with a rotor member to form expansible working chambers therein, a cam ring located radially outwardly from said rotor member and having an inwardly facing cam surface arranged to cooperate with said working members, a rear cover mounted laterally of said rotor member and its said working chambers and extending transversely of the axis of the said rotor member, a valve plate mounted between said rear cover and said working chambers, said rear cover having an inner side surface extending transversely of the axis of said rotor member and facing toward said working chambers, and an outer side surface facing in the opposite direction, said rear cover having an annular recess in an inner side surface and a plurality of radially spaced annular grooves opening to said annular recess and disposed outwardly from said working chamber relative to said annular recess and having a plurality of working fluid outlet and inlet ports extending from said annular grooves to its outer side surface, said valve plate being seated within said annular recess in said rear cover and forming a cover for said annular grooves and being slidable relative to the surface of said rotor member about the axis of the said rotor member, said rotor member having working fluid passages each communicating between one of said working chambers at the interface of the contacting surfaces between said rotor member and said valve plate, said valve plate having a plurality of passages ex- I to tending therethrough and each of said passages arranged to interconnect one of said working passages to one of said annular grooves and the slidable relationship of said valve plate relative to said rotor member affording a change in the connection of the said working fluid passages through said passages in said valve plate with said annular grooves in said rear cover and said inlet and outlet ports communicating with said annular grooves, an annular channel formed in said rear cover and spaced between and from two adjacent ones of said annular grooves and open at one end to said annular recess in said rear cover so that said valve plate extends across said annular channel and said annular channel extends therefrom toward but spaced from the outer side surface of said rear cover, a duct formed in said rear cover and spaced outwardly from said annular recess in the direction toward the outer side surface of 

1. A fluid motor or fluid pump comprising a plurality of working members cooperating with a rotor member to form expansible working chambers therein, a cam ring located radially outwardly from said rotor member and having an inwardly facing cam surface arranged to cooperate with said working members, a rear cover mounted laterally of said rotor member and its said working chambers and extending transversely of the axis of the said rotor member, a valve plate mounted between said rear cover and said working chambers, said rear cover having an inner side surface extending transversely of the axis of said rotor member and facing toward said working chambers, and an outer side surface facing in the opposite direction, said rear cover having an annular recess in an inner side surface and a plurality of radially spaced annular grooves opening to said annular recess and disposed outwardly from said working chamber relative to said annular recess and having a plurality of working fluid outlet and inlet ports extending from said annular grooves to its outer side surface, said valve plate being seated within said annular recess in said rear cover and forming a cover for said annular grooves and being slidable relative to the surface of said rotor member about the axis of the said rotor member, said rotor member having working fluid passages each communicating between one of said working chambers at the interface of the contacting surfaces between said rotor member and said valve plate, said valve plate having a plurality of passages extending therethrough and each of said passages arranged to interconnect one of said working passages to one of said annular grooves and the slidable relationship of said valve plate relative to said rotor member affording a change in the connection of the said working fluid passages through said passages in said valve plate with said annular grooves in said rear cover and said inlet and outlet ports communicating with said annular grooves, an annular channel formed in said rear cover and spaced between and from two adjacent ones of said annular grooves and open at one end to said annular recess in said rear cover so that said valve plate extends across said annular channel and said annular channel extends therefrom toward but spaced from the outer side surface of said rear cover, a duct formed in said rear cover and spaced outwardly from said annular recess in the direction toward the outer side surface of said rear cover for affording communication between said channel and the adjacent one of said annular grooves acting at the higher pressure of the two adjacent ones of said annular grooves, and a ring seated within said channel and arranged in contact with the surface of said valve plate covering said annular groove so that leakage of fluid is avoided by virtue of the pressure differential between the adjacent one of said annular grooves. 